The amorphous carbon film is a rigid film called diamond-like carbon (hereinafter referred to as DLC). As the essential quality of the DLC film, the DLC film has a structure intermediate between diamond and graphite. The DLC film has a high hardness comparable to diamond and is excellent in its wear resistance, lubricity, thermal conductivity, chemical stability, and corrosion resistance. Therefore the DLC film is utilized as a protection film of dies, tools, abrasive materials, mechanical parts, and the like.
As methods for forming the amorphous carbon film (DLC film), a method to be carried out by utilizing arc discharge between carbon electrodes (see patent document 1), a cathode discharge ion plating method to be carried out by using a carbon target (see patent document 2), and an unbalanced magnetron sputtering (hereinafter referred to as UBMS) are adopted. In these methods, films are all formed under a high vacuum.
There is proposed an art of forming the amorphous carbon film (DLC film) by using a power source for a bipolar plasma-based ion implantation (hereinafter referred to as PBII) apparatus (see patent document 3). In this method, a negative voltage is applied to an electrically conductive base material in hydrocarbon plasma to deposit hydrocarbon radicals and ions on the surface thereof. In this manner, a film is formed. Positive high voltage pulses are applied to the base material to irradiate the surface layer thereof being formed with electrons in plasma at a high energy so that only the surface layer thereof is activated and has a high temperature by applying the positive high voltage pulses thereto. This method provides the amorphous carbon film excellent in its corrosion resistance and adhesiveness. In this method, toluene is used as the material gas, and the film is formed under a high vacuum having a vacuum degree of about 0.02 Pa.